In a screw compressor that compresses a gas using a pair of male and female screw rotors, a rotor shaft driven by a motor or the like passes through a rotor casing that houses the rotors, but it is extremely difficult to create a perfect seal between the rotor shaft and the rotor casing. To prevent coolant leaks in a screw compressor that compresses such a coolant, a hermetically sealed structure is often used, in which a compressor main body and the motor are integrally connected, or in other words, the rotor casing that houses the screw rotors is integrally connected with the stator of the motor and a motor casing that houses the rotor, and the coolant that leaks from gaps between the rotor shaft and the rotor casing is thus sealed within the motor casing.
In such a hermetically sealed compressor, the gas to be compressed enters into the motor casing, and thus it is necessary for the coils of the motor to be resistant to corrosion in the case where a corrosive gas is to be compressed. Accordingly, a technique in which aluminum wires covered with a fluorine resin are used for the coils of a screw compressor motor in a refrigeration device that employs ammonia as a coolant is known, as disclosed in, for example, Patent Document 1. Aluminum wires have a higher resistivity than typical copper wires, and thus it is necessary to increase the diameter of the coils in order to reduce the coil resistance.
As disclosed in Patent Document 2, the leading ends of the stator coils (that is, lead wires) are connected to respective external terminals (external terminals) that pass through a terminal block that seals the opening of the motor casing, in order to supply electricity to the stator coils from the exterior. Normally, external terminals have crimped terminal structures in which the leading ends of the coils are inserted and crimped.
Because it is necessary for the motor casing to be able to withstand pressure, the terminal block cannot be made very large. Furthermore, generally speaking, it is desirable for the terminal block to be able to be used in a variety of different products to enable the standardization of components. For this reason, if aluminum wires that have larger diameters than copper wires are connected to external terminals arranged at the same pitch as in a normal motor, the distance between the crimped areas of the external terminals will be shorter. Meanwhile, ammonia is less insulative than air, and thus there is a problem in that if the distance between the crimped areas of the external terminals becomes shorter, insulation breakdown will occur within the motor, resulting in shorts.
Furthermore, if the diameter of the aluminum wires is increased, it is difficult, when crimping a plurality of aluminum wires or aluminum stranded wires to the external terminals, to ensure that a strong compressive force extends to the center of the bundle of wires or stranded wires; as a result, gaps are produced in the approximate center of the plurality of aluminum wires, the center of the aluminum stranded wires, and the like. If such is the case, there will be insufficient conductive contact between the filaments in the center and the filaments on the outside, leading to more current flowing through the outside; this results in high local Joule loss, which carries the risk of lead wire burnout. Such heat generation can be prevented by increasing the diameter of the lead wires, increasing the dimensions of the external terminals, or the like, but doing so further reduces the insulation distance and increases the risk of shorts.